1. Field of the Invention
This invention relates to a method for the manufacture of a hollow fiber. More particularly, this invention relates to a novel method for the manufacture of a hollow fiber for dialysis which is used as in the artificial kidney and the like.
2. Description of Prior Arts
Recently, artificial kidneys utilizing the action of osmosis and that of ultrafiltration have been making remarkable progress and are widely utilized in the field of medical treatments. In such artificial kidneys, very fine hollow fibers for dialysis constitute the most important component member.
The hollow fibers for dialysis are represented by (1) a hollow fiber having a uniform wall thickness of several .mu.m, to 60 .mu.m and a uniform truly circular cross section of 10 .mu.m to some hundred .mu.m of outside diameter throughout the entire fiber length and the entire circumference, having an oriented texture, and continuously pierced throughout the entire extent of the fiber (Japanese Patent Publication No. 40168/1975), (2) a man-made hollow fiber formed of cuprammonium regenerated cellulose in a cross-sectional construction such that the portion of cellulose close to the outer surface has a denser porous structure than the portion of cellulose close to the inner surface and the intermediate portion of cellulose (Japanese Patent Publication No. 1363/1980), and (3) a hollow fiber for dialysis made of cuprammonium regenerated cellulose in the shape of a tube containing a hollow core such that, in observation under an electron microscope, the entire lateral and longitudinal cross sections show a substantially homogeneous, fine porous structure containing minute pores of at most 200 .ANG. and skinless, smooth surfaces on both inner and outer boundaries (Japanese Patent Publication No. 134920/1974). All of these hollow fibers are produced invariably by extruding a spinning dope of cuprammonium cellulose through an annular spinning nozzle into the ambient air and allowing the extruded tubular fiber of spinning dope to fall downwardly by its own weight and, at this point, introducing a non-coagulant liquid relative to the spinning dope to fill the inner core of the tubularly extruded fiber of spinning dope thereby allowing the tubular fiber to be thoroughly drawn out by the fall due to the gravitational attraction, and thereafter immersing the tubular fiber into a bath of dilute sulfuric acid thereby coagulating and regenerating the cuprammonium cellulose in the tubular fiber.
To make a device for dialysis such as an artificial kidney from such a hollow fiber there is adopted a procedure which involves inserting a bundle of hollow fibers in a tubular body provided with an inlet tube and an outlet tube near the opposite extremities thereof and sealing the opposite extremities of the bundle together with the opposite extremities of the tubular body with a resin such as of polyurethane. The device thus produced has a construction resembling a shell and tube type device such as is used in a heat exchanger.
As described above, the conventional hollow fibers are produced by the steps of extruding a spinning dope of cuprammonium cellulose into a gaseous atmosphere such as of air, allowing the extruded tubular fiber to fall by its own weight, and thereafter immersing the tubular fiber in a coagulant liquid thereby coagulating and regenerating the cellulose in the fiber. While the tubular fiber of spinning dope is falling through the gaseous atmosphere, therefore, ammonia separates to some extent from the fiber and begins to coagulate in the surface region of the fiber. Consequently, the produced hollow fibers invariably form a skin on the outer surface, though to varying degrees depending on the particular method of manufacture. Thus, the produced fibers do not acquire a uniform texture throughout the inner and outer surface regions and the intermediate region. When such hollow fibers are used in a device for dialysis, since the fine pores formed in the inner surface region, the intermediate region, and the outer surface region have different diameters, the fiber properties are not fixed in the direction of the wall thickness of the individual hollow fibers. The device, therefore, has a disadvantage that it fails to provide required dialysis with satisfactory results. Further in the conventional method described above, since the spinning nozzle is inevitably exposed to the gaseous atmosphere, the temperature of the spinning dope just discharged from the spinning nozzle and that of the non-coagulant liquid introduced in the inner core of the extruded fiber of spinning dope are difficult to control.
Further in the conventional method, if the non-coagulant liquid placed inside the fiber of spinning dope tubularly extruded through the spinning nozzle leaks, the leaking liquid floats on the upper layer of the coagulant liquid. When the tubular fiber of spinning dope is immersed into the coagulant liquid, therefore, it inevitably passes through the non-coagulant liquid layer. This contact with the non-coagulant liquid forms a possible cause for breakage of the hollow fiber.
Accordingly, an object of the present invention is to provide a novel method for manufacture of a hollow fiber.
Another object of the present invention is to provide a method for the manufacture of a hollow fiber having a perfectly homogeneous texture throughout the inner and outer surface regions as well as in the intermediate region.
Still another object of the present invention is to provide a method for the manufacture of a hollow fiber having good production environment, high safety to fire and proving inexpensive.